Fluidic compressor air bleed valve control apparatus

ABSTRACT

Gas turbine engine compressor air bleed valve control apparatus includes a flow circuit having two series flow restrictions through which a small flow of compressor pressurized air is vented from the compressor air bleed location to the compressor air inlet and between which restrictions a reference air pressure is generated. During an engine acceleration compressor discharge air pressure is compared to the reference air pressure and, upon reaching a predetermined ratio of the same corresponding to a selected engine speed, the bleed valve is actuated in a closing direction to maintain the predetermined ratio constant as engine acceleration continues until a second engine speed is attained at which the bleed valve is closed. The engine speed at which the bleed valve actuation is initiated and the range of engine speeds required to fully close the bleed valve may be varied to suit requirements of a given engine.

United States Patent 1 [111 3,849,020

Eastman Nov. 19, 1974 FLUIDIC COMPRESSOR AIR BLEED Primary Examiner-C..l. Husar VALVE CONTROL APPARATUS Attorney, Agent, or Firm-Gordon H.Chenez; William N. Antonis [75] Inventor: James M. Eastman, South Bend,

Ind.

[73] Assignee: The Bendix Corporation, South [57] ABSTRACT Bend, Gasturbine engine compressor air bleed valve control 22 F1 d: Se L131973apparatus includes a flow circuit having two series 1 m p flowrestrictions through which a small flow of com- PP N08 396,905 pressorpressurized air is vented from the compressor air bleed location to thecompressor air inlet and be- 52 us. on. 4115/28 60/3927 twee" whichrestrictions 3 reference air Pressure is 51 int. cu. ..Fi)1b 25/00generated- During an engine acceleration compressor [58] Field of SearchU 415/28 /3927 discharge air pressure is compared to the reference airpressure and, upon reaching a predetermined ratio of [56] ReferencesCited the same corresponding to a selected engine speed, the bleed valveis actuated in a closing direction to UNITED STATES PATENTS maintain thepredetermined ratio constant as engine 2,950,596 8/1960 Haase et all60/3928 acceleration continues until a second engine Speed is 2 gattained at which the bleed valve is closed. The engine 3487993 141970gz i g speed at which the bleed valve actuation is initiated 3488948H1970 Comm at and the range of engine speeds required to fully close3Is09I490 5/1974 Harner 4l5/28 thebleed velve may be varied to Suitrequirements of a given engine.

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BACKGROUND OF THE INVENTION The present invention is an improvement overthe compressor bleed valve actuator shown and described in U.S.Application Ser. No. 347,251 filed Apr. 2, 1973 (common assignee). Inparticular, the present invention is less complex structurally, lessexpensive to manufacture, lighter in weight and smaller in volume thanthat of said Application Ser. No. 347,251.

It will be recognized that the conventional multistage axial flow aircompressor for a gas turbine engine is provided with matched stages foroptimum performance at the design engine speed and compressor pressureratio. Obviously, at lower engine operating speeds and for engineaccelerations and decelerations, the compressor must function atsubstantially lower compression ratios as a result of which the airdensity in the rear stages of the compressor is not increased over theair densities in the front stages of the compressor by as high a ratioas exists at design speed. Thus, the volumetric flow rates in the rearstages become a larger fraction of those in the front stages as enginespeed decreases which, in turn, results in a corresponding unloading" ofthe rear stages and a loading up of the front stages resulting in ashifting of the compression ratio burden to the front stages tending todrive the same into the well known compressor phenomenon known as stall.

Various control devices are known which are used to avoid theabove-mentioned undesirable tendency of the compressor to load up. Ingeneral, conventional control devices may be classified as (1) variableinlet guide vanes which selectively change compressor stage geometry asa function of engine speed, and (2) compressor bleed valves which areopened to vent pressurized air from an associated compressor front orintermediate stage to a relatively lower pressure air source to therebyunload the stages upstream of the bleed valves.

In comparison to variable inlet guide vanes, the compressor bleed valveis less efficient but has the advantages of reliability, simplicity andlower cost. However, the reduced efficiency of the bleed valve may betolerated providing air bleeding is not required at normal operatingengine speeds for extended periods of operation and/or does notadversely sacrifice acceleration torque.

Prior art compressor bleed valve control apparatus of which I am awareinclude U.S. Pat. No. 3,172,259, issued Mar. 9, 1965 to Howard L. North,.Ir., and U.S. Pat. No. 3,646,753, issued Mar. 7, 1972 to Michael E.Coleman et al. which are not entirely satisfactory for various reasons,including structural complexity, weight and/or bulky nature as well astwo position operation wherein the bleed valve is snapped open or closedwhich has an undesirable effect in that it tends to cause a thrust orpower discontinuity in engine operation and/or operation over a morenarrowly adjustable range of engine corrected speed.

It has been found that thrust continuity and speed holding stability maybe maintained with minimum efficiency penalty by controlling the bleedvalve such that it is progressively opened or closed, depending uponengine deceleration or acceleration, over a suitable range of compressoror engine corrected speed (N/ VF) wherein N is rotational speed of thecompressor and 6 is compressor inlet air temperature divided by standardatmospheric air temperature (519 R). Since the compression ratio of thecompressor is a known function of corrected engine speed, thecompression ratio may be utilized to advantage as a substitute ofcorrected engine speed for control purposes.

SUMMARY OF THE INVENTION It is an object of the present invention toprovide gas turbine engine multiple stage air compressor bleed valvecontrol apparatus which is simple in structure, reliable in operationand relatively inexpensive to manufacture.

It is another object of the present invention to provide gas turbineengine multiple stage air compressor bleed valve control apparatus whichopens or closes the bleed valve in proportion to corrected engine speedover a predetermined range of engine speeds.

It is an important object of the present invention to provide gasturbine engine multiple stage axial flow air compressor controlapparatus which is primarily fluidic in operation and responsive tocompressor compression ratio as defined by compressor inlet and outletpressures.

Other objects and advantages of the present invention will be apparentfrom the following description taken with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS (N/ VF).

DESCRIPTION OF THE PREFERRED EMBODIMENT Referring to FIG. 1, inparticular, numeral 20 designates a conventional gas turbine engineprovided with an air inlet 22 upstream from a multiple stage axial flowair compressor 24 which discharges pressurized air flow to one or morecombustion chambers 26. Hot motive gas generated in the combustionchambers 26 and discharged therefrom is passed through a gas turbine 28connected to drive the air compressor 24 via a shaft 30. The dischargegas from the gas turbine 28 is expelled through a discharge nozzle 32thereby providing a propelling thrust.

A controlled rate of fuel flow is supplied to combustion chambers 26 viafuel injection nozzles 34 supplied pressurized fuel by a fuel manifold36 connected thereto and provided with a fuel supply conduit 38 leadingfrom the outlet of a fuel control generally indicated by 40. The fuelcontrol 40 is. adapted to receive control input signals including enginerotational speed N, via suitable gear and shafting 42, power request viaa throttle lever 44 and compressor pressurized air at pressure P via aconduit 46 providing fluid communication between control 40 and thedischarge section of compressor 24.

One or more conventional compressor air bleed valves 48 suitablyconnected to a selected stage or stages of the compressor 24 and adaptedto vent compressor pressurized air therefrom to a suitable relativelylow pressure drain source such as the compressor inlet 22 is actuated bycontrol means generally indicated by 50.

Referring to FIG. 2, in particular, there is shown sections of inner andouter spaced apart casing portions 52 and 54, respectively, of enginewhich surround compressor 24. The inner casing portion 52 is immediatelyadjacent the compressor rotor, not shown, and provided with an opening56 adapted to receive a bleed valve retaining member 58 which isprovided with a valve seat 60 through which compressor pressurized airat pressure P is vented to an annular duct 62 between casing portions 52and 54. The annular duct 62 is vented to the compressor inlet 22. and ismaintained at relatively low inlet air pressure P A poppet valve 64 isprovided with oppositely extending stems 66 and 68 and is adapted toseat against valve seat 60 to thereby control the flow of pressurizedair through seat 60. The stem 68 is slidably supported in a support orguide bracket 70 integral with retaining member 58. The poppet valve 64is actuated by a diaphragm 72 fixedly secured to stem 66 by a backingplate 74 against which a nut 76 threadedly engaged with stem 66 bears.The radially outermost portion of diaphragm 72 is clamped betweenretaining member 58 and a cap 76 which cap 76 is fixedly secured inposition by a plurality of bolts 78 extending therethrough into threadedengagement with retaining member 58.

The cap 76 is defined by a casing 80 housing a conventional pure fluidamplifier 82 of the proportionally acting type wherein a power fluid jet84 discharged from an inlet port 86 toward a pair of outlet ports 88 and90 passes between opposed control ports 92 and 94 which are suppliedpressurized fluid as will be described to deflect the powerjet 84relative to outlet ports 88 and 90 thereby increasing the flow to andthus pressurization of one outlet port and decreasing the flow to andthus pressurization of the other outlet port in proportion to thecontrol pressure differential generated at control ports 92 and 94. Inthe absence of a pressure differential at control ports 92 and 94 thepower jet 84 will occupy a null position thereby pressurizing outletports 88 and 90 accordingly. Reference is made to U.S. Pat. No.3,486,520 issued Dec. 30, 1969 in the name of]. M. l-lyer et a]. for aproportional type fluid amplifier suitable for use as amplifier 82.

The inlet port 86 is provided with a restriction 96 which is suppliedpressurized air at compressor discharge pressure P via a passage 98containing a fixed restriction 100 and leading to a port 102 which, inturn, is connected to a passage 104 loading to the discharge portion ofcompressor 24. The outlet port 88 is connected via a passage 106 to achamber 107 partially defined by diaphragm 72. The outlet port 90 isconnected via a passage 108 containing a venturi type flow restriction110 to ambient or atmospheric air pressure P,,. A fixed restriction 112provides fluid communication between passages 106 and 108. The controlport 92 is connected via a passage 114 containing a fixed restriction116 to compressor pressurized air at pressure P at the upstream side ofpoppet valve 64. The passage 114 on the downstream side of restriction116 is vented to compressor inlet air pressure P, via a passage 118containing a fixed restriction 120. A passage 122 containing a fixedrestriction 124 and a venturi type restriction 126 connects port 102with ambient or atmospheric air pressure P,,. The control port 94 isconnected via a passage 127 to passage 122 intermediate restrictions 124and 126.

Referring to FIG. 3, first and second sources of curves are plotted forvarious pressure ratios P P3111, pg p pg p and P p wherein P3 designatesCompressor discharge pressure, P, designates compressor inlet airpressure, P, designates compressor pressurized air at a given compressorstage where the bleed or poppet valve 64 is located, and P, designatesthe air pressure generated intermediate the fixed restrictions 116 and120. The curve labeled P represents the over-all compression ratio ofcompressor 24; curve labeled P represents the compression ratio for thecompressor stages aft of the bleed valve 64; curve labeled Pg prepresents the compression ratio for the compressor stages forward ofthe bleed valve 64 and curve P illustrates the relationship of the ratioof pressures P and P to the other pressure ratio curves. The open seriesof curves terminate at a first predetermined corrected engine speed, A,and the closed series of curves start at a second predetermined highercorrected engine speed, B. Intermediate the first and secondpredetermined engine speeds the bleed or poppet valve 64 is caused toclose in proportion to increasing engine speed from A to B.

It will be noted from the P and P curves that the gain in compressionratio for the forward stages corresponds closely to the loss incompression ratio for the aft stages of the compressor 24 following theclosing of bleed or poppet valve 64.

It will be assumed that the engine 20 is undergoing an accelerationthrough the speed range from below A to above B. Compressor dischargeair at pressure P is passed through fixed restrictions 116 and 120 torelatively lower pressure compressor inlet air P thereby generating anintermediate pressure P, which varies in accordance with therelationship P, a f(P /P l wherein the function f is determined by thearea ratio of fixed restrictions 116 and 120 as will be recognized bythose persons skilled in the appropriate art. Reference is made to U.S.Pat. No. 2,950,596 issued Aug. 30, 1960 to E. A. Haase et al. fordetails of flow through two fixed restrictions in series flowrelationship. Referring to FIG. 3, the curve labeled P illustrates themanner in which pressure P varies in response to the increasing enginespeed.

The compressor discharge air at pressure P is passed through fixedrestrictions 124 and venturi 126 to ambient or atmospheric air pressureP thereby generating an intermediate pressure Py which, with sonic flowthrough venturi 126, is a fixed percentage of pressure P as is wellknown in the art. The pressure P is applied to control port 92 where itacts against power jet 84 in opposition to the lesser pressure P appliedto control port 94 thereby deflecting the power jet 84 toward controlport 94 which results in the major portion of the power jet 84 passingthrough outlet port and venturi to atmospheric air pressure P,,. Theoutput pressure P at outlet port 88 is decreased accordingly and passesto chamber 107 where it acts against diaphragm 72 in opposition tocompressor inlet air pressure P,. The force derived from the pressuredifferential P P acting across diaphragm 72 is overcome by the forcederived from the pressure differential P P, acting across bleed orpoppet valve 64 which urges poppet valve 64 to an open position therebyventing compressor pressurized air at pressure P to compressor inlet airpressure P,. It will be recognized that poppet valve 64 will be balancedby P P in accordance with the relationship P P Av/A (P P wherein Avdesignates the effective area of valve 64 and A designates the effectivearea of diaphragm 72.

The pressure Py and P, increase and become equalized at predeterminedengine speed A whereupon power jet 84 is caused to assume its nullposition which results in an increase in outlet pressure P; and thus P Ppressure differential across diaphragm 72 thereby establishing a forcebalance on poppet valve 64. As engine acceleration progresses beyondengine speed A, the pressure Py increases at a greater rate thanpressure P; thereby deflecting power jet 84 from its null positiontoward control port 92, resulting in an increase in outlet pressure Pwhich, in turn, results in a force unbalance on poppet valve 64 tendingto close the same. As poppet valve 64 moves in a closing direction, thepressure P is increased accordingly tending to reestablish a forcebalance on poppet valve 64. In this manner, poppet valve 64 is caused toclose progressively in response to increasing engine speed as the engineaccelerates from engine speed A to B. Upon reaching engine speed B, thepoppet valve 64 is fully closed thereby blocking air flow through theseat. It will be noted that the ratio of Pressures P is controlled to aconstant value from engine speed A to B by virtue of the closing ofpoppet valve 64 and resulting effect on pressure P As a result, asubstantially linear relationship will exist between the position ofpoppet valve 64 and corrected engine speed N/ VF'over the speed rangedefined by A and B.

With poppet valve 64 closed, no further control over pressure P can beexercised and the pressure ratio P increases with increasing speed, asshown in FIG. 3, with the result that pressure Py exceeds pressure P tothe extent that power jet 84 is maintained in an offnull positiontending to increase pressure P; to a maximum. Thus, the force tending tohold poppet valve 64 closed is maintained in excess of the opposingforce derived from P P as the engine accelerates from engine speed B tothe selected speed.

In the case of reverse operation, i.e., an engine deceleration, it willbe recognized that the poppet valve 64 will be caused to openprogressively from B to A. Upon reaching engine speed A, the forceunbalance imposed on poppet valve 64 will increase to maintain poppetvalve 64 in the maximum open position at engine speeds below point A.

It will be understood that the spread between engine speeds A and B maybe adjusted to suit the characteristic of a given engine. To that end,the fixed restriction 116 may be plugged thereby making P, equal topressure P in which case the poppet valve 64 will tend to operate at afixed P pressure ratio resulting in little or no engine speed spreadbetween open and closed positions of poppet valve 64. However, if fixedrestriction 120 is plugged thereby making pressure P; equal to pressureP the poppet valve 64 will operate at a fixed P ratio resulting in arelatively large engine speed spread between open and closed positionsof poppet valve 64. Obviously, the ratio of areas of fixed restrictions116 and 120 may be selected to generate a pressure P which is closer topressure P or P thereby ingine speeds between points A and B.

It will be noted that the area ratio of fixed restriction 124 andventuri 126 also has an effect on the operation of poppet valve 64. Forexample, the ratio of fixed restriction 124 to venturi 126 may beincreased thereby reducing the ratio of pressure P to pressure P Thisresults in a lower ratio of pressures Pg/P regulated by poppet valve64in view of pressure P, being equal to pressure P at null. Referring toFIG. 3, it is apparent that a reduction in the equilibrium ratio ofpressures Pgg/p reduces the engine speeds at which poppet valve 64action occurs. Thus, by suitable selection of the ratio of areas ofrestrictions 120 and 116 and/or ratio of areas of fixed restriction 124and venturi 126 the poppet valve 64 operation may be adjusted to meetthe requirements of a given engine.

The air flows from outlet ports 88 and 90 of fluidic amplifier 82 arevented via choked venturi restriction 110 to atmospheric air pressure PIt will be recognized that by suitable selection of the effective flowareas of fixed restriction 86 and venturi 110, the supply air pressure Pintermediate restrictions and 86 and the vent pressure P intermediateoutlet port 88 and venturi restriction may be controlled in an optimumratio with compressor discharge air pressure P to provide bestperformance of the amplifier 82 as well as assure that the pressure Psupplied to diaphragm 72 is well within the saturation limits ofamplifier 82. If the vent pressure P was equivalent to pressure P,, thesubstantial ratio increase of P relative to the ratio increase of P asthe poppet valve 64 moves in a closing direction, would require a largeincrease in the amplifier 82 null output pressure recovery P, P /P Pthereby taxing the capabilities of conventional fluidic amplifiers.However, by making vent pressure P a fixed fraction of pressure P thevent pressure P may be made to equal pressure P for the open conditionof poppet valve 64 and significantly larger for the closed condition ofpoppet valve 64 thus not requiring as great a pressure recovery fractionfor pressure P at equilibrium of poppet valve 64.

I claim:

1. Gas turbine engine air compressor bleed valve apparatus comprising:

valve means operatively connected to said air compressor for ventingcompressor pressurized air from a compressor stage intermediate thecompressor inlet and outlet to a relatively lower pressure air source;

first pressure responsive means responsive to the pressure differentialbetween said compressor pressurized air and said relatively lowerpressure air operatively connected to said valve means for actuating thesame in an opening direction;

second pressure responsive means responsive to the pressure differentialbetween a control air pressure and said relatively lower air pressureoperatively connected to said valve means for actuating the same in aclosing direction;

a first passage having first and second series flow restrictionscommunicating compressor discharge air with a relatively lower pressureair source;

a second passage having third and fourth series flow restrictionscommunicating compressor pressurized air from said intermediate stage tocompressor inlet air;

fluid pressure differential responsive control means a zero pressuredifferential therebetween.

responsive to the pressure differential between a 3. Gas turbine engineair compressor air bleed valve first fluid pressure generated betweensaid first and apparatus as claimed in claim 2 wherein: second flowrestrictions which varies as a predetersaid other outlet port isconnected to said relatively mined function of compressor pressure ratioand low pressure drain air source via a third passage thus compressorcorrected rotational speed and a containing a fifth restriction; secondfluid pressure generated between said third said outlet port vented tosaid second pressure reand fourth flow restrictions said control meanssponsive means is further vented via a restriction to adapted to controlsaid control air pressure in prosaid third passage upstream from saidfifth restricportion to said fluid pressure differential derived 10tion. from said first and second fluid pressures; 4. Gas turbine engineair compressor air bleed valve said valve means being actuated to afully open posiapparatus as claimed in claim 1 wherein:

tion in response to said control air pressure at comsaid secondrestriction is a venturi. pressor corrected rotational speeds below aprede- 5. Gas turbine engine air compressor air bleed valve terminedvalve and progressively actuated to a fully apparatus as claimed inclaim 1 wherein: closed position over a predetermined range of saidsecond and fourth restrictions are venturis. compressor correctedrotational speeds during an 6. Gas turbine engine air compressor bleedvalve apengine acceleration. paratus as claimed in claim 1 wherein:

2. Gas turbine engine air compressor air bleed valve said relativelylower pressure air source is compresapparatus as claimed in claim 1wherein: sor inlet air.

said fluid pressure differential responsive control 7. Gas turbineengine air compressor air bleed appameans includes a source ofcompressor pressurized ratus as claimed in claim 1 wherein: air; saidvalve means is a poppet valve;

a pair of outlet ports one of which is vented to said said firstpressure responsive means is defined by the second pressure responsivemeans and the other of head portion of said poppet valve. which isvented to a relatively low pressure drain 8. Gas turbine engine aircompressor air bleed appaair source; ratus as claimed in claim 7wherein:

a deflectable air jet derived from said last named said second pressureresponsive means is a diacompressor pressurized air and directed towardphragm fixedly secured to said poppet valve.

said outlet ports to pressure the same to a variable 9. Gas turbineengine air compressor air bleed appa degree depending upon thedeflection thereof; and ratus as claimed in claim 1 wherein:

said first and second restrictions have a predetera pair of opposedcontrol air ports one of which is mined fixed area ratio.

connected to said first passage intermediate said 10. Gas turbine engineair compressor air bleed appafirst and second restrictions and the otherof which ratus as claimed in claim 1 wherein: is connected to saidsecond passage intermediate said first and second restrictions have apredetersaid third and fourth restrictions; mined fixed area ratio; andsaid deflectable air jet being responsive to the air said third andfourth restrictions have a predeterpressure differential between saidpair of control mined fixed area ratio. air ports and having a nullposition in response to its

1. Gas turbine engine air compressor bleed valve apparatus comprising:valve means operatively connected to said air compressor for ventingcompressor pressurized air from a compressor stage intermediate thecompressor inlet and outlet to a relatively lower pressure air source;first pressure responsive means responsive to the pressure differentialbetween said compressor pressurized air and said relatively lowerpressure air operatively connected to said valve means for actuating thesame in an opening direction; second pressure responsive meansresponsive to the pressure differential between a control air pressureand said relatively lower air pressure operatively connected to saidvalve means for actuating the same in a closing direction; a firstpassage having first and second series flow restrictions communicatingcompressor discharge air with a relatively lower pressure air source; asecond passage having third and fourth series flow restrictionscommunicating compressor pressurized air from said intermediate stage tocompressor inlet air; fluid pressure differential responsive controlmeans responsive to the pressure differential between a first fluidpressure generated between said first and second flow restrictions whichvaries as a predetermined function of compressor pressure ratio and thuscompressor corrected rotational speed and a second fluid pressuregenerated between said third and fourth flow restrictions said controlmeans adapted to control said control air pressure in proportion to saidfluid pressure differential derived from said first and second fluidpressures; said valve means being actuated to a fully open position inresponse to said control air pressure at compressor corrected rotationalspeeds below a predetermined valve and progressively actuated to a fullyclosed position over a predetermined range of compressor correctedrotational speeds during an engine acceleration.
 2. Gas turbine engineair compressor air bleed valve apparatus as claimed in claim 1 wherein:said fluid pressure differential rEsponsive control means includes asource of compressor pressurized air; a pair of outlet ports one ofwhich is vented to said second pressure responsive means and the otherof which is vented to a relatively low pressure drain air source; adeflectable air jet derived from said last named compressor pressurizedair and directed toward said outlet ports to pressure the same to avariable degree depending upon the deflection thereof; and a pair ofopposed control air ports one of which is connected to said firstpassage intermediate said first and second restrictions and the other ofwhich is connected to said second passage intermediate said third andfourth restrictions; said deflectable air jet being responsive to theair pressure differential between said pair of control air ports andhaving a null position in response to a zero pressure differentialtherebetween.
 3. Gas turbine engine air compressor air bleed valveapparatus as claimed in claim 2 wherein: said other outlet port isconnected to said relatively low pressure drain air source via a thirdpassage containing a fifth restriction; said outlet port vented to saidsecond pressure responsive means is further vented via a restriction tosaid third passage upstream from said fifth restriction.
 4. Gas turbineengine air compressor air bleed valve apparatus as claimed in claim 1wherein: said second restriction is a venturi.
 5. Gas turbine engine aircompressor air bleed valve apparatus as claimed in claim 1 wherein: saidsecond and fourth restrictions are venturis.
 6. Gas turbine engine aircompressor bleed valve apparatus as claimed in claim 1 wherein: saidrelatively lower pressure air source is compressor inlet air.
 7. Gasturbine engine air compressor air bleed apparatus as claimed in claim 1wherein: said valve means is a poppet valve; said first pressureresponsive means is defined by the head portion of said poppet valve. 8.Gas turbine engine air compressor air bleed apparatus as claimed inclaim 7 wherein: said second pressure responsive means is a diaphragmfixedly secured to said poppet valve.
 9. Gas turbine engine aircompressor air bleed apparatus as claimed in claim 1 wherein: said firstand second restrictions have a predetermined fixed area ratio.
 10. Gasturbine engine air compressor air bleed apparatus as claimed in claim 1wherein: said first and second restrictions have a predetermined fixedarea ratio; and said third and fourth restrictions have a predeterminedfixed area ratio.